Apparatus for determining the velocity of a target, especially aircraft



Juli-30, 1940.

APPARATUS FOR DETERMINING THE VELOCITY OF A TARGET, ESPECIALLY AIRCRAFT Filed June 21, 1938 l 2 Shaets-Sheet 1 J. Tlcl-nf 2,209,485

APPARATUS FOR DETERMINING THE VELOCITY 10F A TARGET, ESPECIALLY AIRCRAFT July 30-, 1940.

Filed June 21, 193a 2 Sheets-Sheet 2 I/VVE/VTO Ta measured, the length of the measuring path be- Patented Jul 30, 1940 UNITED STATES- PATENT OFFICE APPARATUS FOR DETERMINING THE VE- LOCITY OF ,A TARGET, ESPECIALLY AIR- CRAFT Josei Tichy, Brunn, Czechoslovakia, assignor to Ceskoslovenska Zbrojovka, a. s.,Brno,

, runn, Czechoslovakia, a company of Czechoslovakia Application June 21, 1938, Serial No. 215,043 I In Czechoslovakia June 18, 1931 5 Claims.

This invention relates to apparatus for determining the velocity of a target, especially aircraft which is moving in a straight line in a horizontal plane.

'obviate the disadvantages of theknown devices and to provide a simple and easily transportable apparatus, which is readily operated, for the purpose of determining more particularly the velocity of aircraft.

According to the present invention,- there is provided apparatus comprising sighting means which, on sighting the target, mark out, by means of the projection into space from a central point of observation, the path on which the velocity is ing at a given ratio to the instantaneous distance of the target from the observer.

The apparatus according to the present invention can also be used on board aircraft either for determining the velocity of the aircraft or. if the velocity'of flight is known, for determining the height of the aircraft above the ground. Inorder that the present invention may be clearly understood and readily can-led into efiect the same will now be described more fully, by way of example, with reference to the accompanying drawings in which:

Figure 1- illustrates diagrammatically the method of determining the velocity of aircraftiby means of apparatus embodying the invention,

Figure 2'is a sectional side elevation of apparatus embodying the invention, Figure 3 is a. vertical cross-sectional view thereof taken on the section line 3-3 01' Fig. 2,

Figures 4 and 5 show in cross-section and in plan, respectively, details of a circular sight of the sighting. device of the apparatus,

Figure 6 is a detail view showing in elevation the scales of the calculating device of 'the apparatus. 7

Referring to the drawings, in Figure 1, L denotes the aircraft which is moving in a straight line with the velocity v in an horizontal plane which is at a height h above'the standing position 0 of the observer. The height h is known and one of the known independent devices is employed for its determination.

The velocity v of a uniiormly'moving point is ascertained by setting up the definite path 8, the 'so-called measuring path,.and by measuring the time t in which the point travels through the path 8. The mean velocity v is given by the ratio I By means of the apparatus according to the present invention, the measuring path s in the path of flight is set up by the pr j ion of h horizontal abscissa from the centre 0 which represents the eye of the observer of the diopter.

There is advantageously chosen as the projection abscissa the radius r of the horizontal circle which is at a definite known ratio, r:d=k, to the distance of the centre M of the circle from the projection centre 0. In the case illustrated, k='0.1.

It is seen from the similarity of the triangles OMB and OLLr that the measuring path s, which .is set up in the path of flight of the aircraft, is in the same ratio to the distance D or the aircraft" as is the radius r of the circle to'the distance d of the centre m of the circle from the point 0,

s:D=r:d==k or In order to be able to ascertain the measuring path s, it is therefore suflicient to determine the distance D of the aircraft, at the beginning of the measurement, from the standing place of the observer. It can be seen that h r where a is-the position angle, which the lineof sight 0L makes with the horizontal plane, and h is the height of the aircraft. This equation is solved mechanically on the apparatus according to the present invention for different position angles a by the geometric adding up of the logarithms on the basis of'the relationship which results from the logarithmislng of the aforesaid equation:

log D=log h-log sin a The velocity locity being likewise eifected on the apparatus trated in Figures 2 to 6.

. lelogram which is tion on which there logarithmically in accordance with the equation.

log o=log s--log t Anexample of a constructional embodiment of the apparatus according to the invention illusi denotes a cylindrical casing to which a base plate I is connected by means of a cotter pin I. The baseplate 2 is adapted to permit the apparatus to be located on a stand (not shown.) For the purpose ofadiusting the casing in a vertical position there is employed a spirit level 4 which is arranged in the base plate 1.

Thecasing I is provided at the top part on the periphery with two lugs 5 (Figures 2 and 3) in which a lever I of the first order is rotatably mounted on a horizontal pin 0. On one arm of the lever I, a diopter l is arranged, and to the other arm of the said lever there is rotatably connected a fixed-circle II, the so-called circular sight (Figure 5), which is provided with crossed.

threads and is always kept in a horizontal position by means of a known device. In the example shown, the said device consists of a paralformed by two levers II and I! which are hingedly connected with each otherand of. which the lever II is connected to the pin cf the circle II and the lever I! is connected tothelugibymeansofapin I3. Theradim! of the circular sight II is equal to 0.1 of the distance d of the diopter from the centre of thecircle ll (Figures 2 and 5).

A cam I with a controlling surface is connected to the lever 1, so that it rotates about the pin 6 coniointiy with the lever. The curvature of the surface is made to depend uponthe angle position min accordance with the equation.

p=ki+ka 108 sins where pv is the polar are constants. .The controlling surface of the cam contacts at its summit with a rod II which ensured by a leaf spring II. The pinion II is keyed on a horizontal-shaft 22 which is mounted in 2| and II in the axis of the cylindricai casing I. The shaft 22 has a square poris fitted a disc wheel 23 with a scale which gives the velocityfor example in metres per second-and the size of the measuring path a in space. circumferenceofthediscwheelflisarlngil which is rotatably mounted in such a manner in the casing I that the front surface of'the ring 2! and the front surface of the disc wheel 2! lie in the same plane. On the ring II there is engraved a scale which gives the height of the aircraftandalsothetimeinseconds andagainst whichthereisarrangedapointer Ilwhichis fixed to the casing I. The opposite side of-the ring II is provided with a ring of teeth ll (H ures2 and3).withwhichapinionll engages. Thepinicnlliskeyedonashaftwhichpames through the cylindrical wallof the casing and is provided with a milled knob 21-" (Figure 2) for the W 1 being rotated'by hand.

crossed threads.

coordinate and hi and In aroundthey controlling cam surface l'is transmitted to smallrod Ilandfromthis,bymeamof shaft. lL-to the disc 28.

2! is held fast in its hearing by means of a lid ll which is secured to the casing I. If desired, the lid may be providedwith a glass II to protect the scale from. dust and effects of the weather.

In order that, by the projection of the circular sight, its image should remain undistorted owing to the thickness of the material, the sight is arranged in the particular manner shown in Figures 4 and 5. The circle It consists of a narrow ring which is constructed in such a manner that the halves of the ring are displaced in relation to each other through a distance equal to the thickness of the material, so that the edges of the'circle, which are projected from the diopter, lie in the same plane X-X. The centre of the circle is indicated by the centre of the crossed threads.

In ascertaining the'velocity v of aircraft by means of the apparatus according to the present invention, the operation is as follows:

After adjusting the apparatus into the vertical position by means of the level 4, sighting the aircraft by meansof the diopter 9 and the circular sight I0 is eifected in such a manner, by the rotation of the whole apparatus about the vertical pin I' as well as by the rotation of the lever I in the plane of elevation, that an aircraft; which is flying in any direction in relation to the observer, is projected into the centre of the While the aircraft is being followed, the cam I and the lever I are in the plane of elevation, so that their movement is directly dependent upon the position angle a.

At the instant in which the desired sighting is obtained, the movement of the apparatus is stopped and is kept in its position by means of. for example, the coupling which connects the fixedrpart of the apparatus with the lever I or by means of another similar. device. At that instant, the measurement, by means of a stop watch, of the time, which the aircraft takes to fly througiii the path LLI, which is proportional t'othe radius of the sight II, is begun. When, during the uninterrupted observation by means of the diopter, the circumference of the circle is reached, the measurement of the time of flight is ended.

The ascertainment of the measuring path s in accordance with the equation It as:

is carried out on the calculating device, which is arranged in the manner of a circular slide rule one scale of which is engraved on the disc 23 and the other is engraved on the ring 2|. The height "I of the aircraft, which is ascertained b an independent apparatus of known construction, is set on the scale of the ring II which is rotated by hand by means of the knob 21 in such a manner that the number that denotes the height of the aircraft comes beneath the pointer On rockingrthe' lever I, the movement of go e rack II, to the pinion l0 and, by means of the quently rotated-in dependence upon the logarithm of the sine of theposition angle a in such a manner that th opposite position of the logarithmic scale gives the desired length of the measuring path a. The numbers which give the measurin ath 2 appear on the scale of. the disc is oppositethe' 2|.

Thediscliiscom The velocity v of the aircraft is ascertained from the equation when the value is read off on the second scale giving the velocity opposite the number denoting the measured time. Since, in logarithmic division, the logarithms are subtracted from each other, the time scale is put on in the reverse direction of the scale of the path s.

In the example of the counting calculating device which is illustrated in Figure 6, the logarithmic scale of heights expressed in hectometres (hm) and the time expressed in seconds on the outer ring 25 and the scale of the path 3 expressed in metres and the velocity of aircraft expressed in metres per second on the disc 23 are advantageously combined. This combina-v tion is possible since all the scales are logarithmic. The following case illustrates an example of measurement with reference to Figure 6:

Let the height of flight h=l000 metres. Consequently, the ring 25 is set in such a manner by the rotation of the knob 21 that the number 10 on its scale comes beneath the pointer 28. After the aircraft is sighted with the apparatus.

the time is measured which the aircraft has taken to fly over the projection of the radius of the circular sight. Let this time t be 4 seconds. The velocity of the aircraft 12:50 metres per second is read off on the velocity scale on the disc 23 opposite the number 4 on the scale of the ring 25.

The manipulation of the apparatus is very simple and the total time that is necessary for the determination of thevelocity of aircraft is only the time that is necessary for the measurement of the time of flight of the aircraft over the radius of the sight. A further great advantage of the apparatusaccording to the invention is, that it is unnecessary to measure the height of flight at the outset but it is possible to carry out the measurement of the height of flight on a separate height meter and then to set the measured height on the apparatus, 50 that the result of the measurement of the velocity of the aircraft is obtained at once. This saving of time is of special importance when the apparatus is used for the determination of firing elements in the case of anti-aircraft guns.

The apparatus does not take up much space, is readily transportable and contains no sensitive components by the injury of which the measurement could be rendered imposible or inaccurate.

The sighting means of the apparatus may be a being possible to carry out the limitation of the measuring path in such a manner by means of a circle that is kept horizontal or by the aid of means arranged in the, telescope that the measuring path is at a definite ratio to the distance of the aircraft from the position at which-the observer is standing. 7

It is possible to use the principle of the apparatus according to the invention for apparatus for other purposes of which there is given as an example an apparatus for the measurement of the height of aircraft above the ground from on board the aircraft. "The method of measurement by means of this apparatus is represented in Figure 9.

Let the aircraft be moving with a known vecentre of the circular sight. the line of sight makes with the horizontal plane,

locity v in a straight line in an horizontal plane is the position angle a. At that instant, the position of the arm of the sighting device is fixed and there is begun the measurement of the time in which the aircraft flies through a .path such that the point C is projected on the edge of the circular sight. At the beginning of the measurement, the aircraft was located at the point A and, during the measurement, it came to the point B and followed the path which is equal to the result of the time and of the velocity, s=v.t.

From the similarity of the triangles MLA and ABC, it can be seen that the path s=v.t. is equal to k: times the distance D of the point C from the initial position A of the aircraft, where k is the ratio of the radius of the sight to the distance of the centre of the sight from the diopter. This, therefore, gives 1 Pp. and, because h=D sin a, it is possible to determine the height from the measured time t, the known velocity v and the position angle a.

The multiplication is effected logarithmically on the calculating mechanism of the apparatus as in the preceding case, log sin u again being given on the apparatus by the controlling earn.

A special case arises if there is always chosen the point C on theground in such a manner that it lies in the vertical plane through the axis of flight. In this case, it is suflicient for the marking out of the path s to have a small section of point C theoretically moves on the small axis of the ellipse.

The forms of the apparatus described and illustrated are obviously only examples of em bodimentsof the invention and it is possible to make various modifications in the construction of the apparatus without departing from the scope of the invention.

What I claim is: v

1. Apparatus for determining the velocity of a target moving rectilinearly in a horizontal plane comprising a base, a member pivoted on said base f on a normally horizontal axis, a circular sight pivoted on said member on an axis coplanar of adiopter on said member coacting with said circular sight to establish a sight line which may be maintained upon the target, relatively movable coacting scales carried by said base and means'interconnecting said scales and said memsaid circular sight and parallel to said first axis,

ber whereby pivoting of said member about its axis effects relative movement of said scales to give a reading thereon of target velocity as the sight line is maintained thereon.

2. Apparatus as set forth in claim 1 in which saidinterconnecting means includes a cam operated synchronously with the pivotal movement of said member whose radial dimensions are proportioned to a trigonometrical function of the angle said sight line makes with the horizontal.

3. Apparatus as set forth in claim 1 in which said scales are respectively located on two circular cooperating discs.

4. Apparatus for determining the velocity of v a target moving recilinearly in a horizontal plane movement of said member whose radial dimensions are proportioned to a trigonometrical function of the angle said sight line makes withthe horizontal, a circular disc having a scale thereon rotatably mounted on said base, a slidably mount-' ed rod on said base actuated by said cam for rotating said disc and a second manually operated circular disc having a scale thereon coacting with said first mentioned scale to give a reading oi. target velocity as the sight line is maintained thereon.

5. Apparatus for determining the velocity 0! a target moving rectilinearly in a horizontal plane comprising a base, a member pivoted on said baseonanormallyhorizontalaxis,a circular sight pivoted on said member on an axis coplanar of said circular sight and parallel'to said first axis. said circular sight having the halves thereof relatively displaced axially of the plane of said circular sight an amount equal to the thickness of the material on both sides oi the axis of said circular sight, a diopter on said member coacting with said circular sight to establish a sight line which may be maintained upon the target, relatively movable coacting scales carried by said base and means interconnecting said scales and said member whereby pivoting or said Josnr' 'ncnir. 

